Known in the art is a machine for driving workings in hard rocks referred to as a heading combine (cf. French Pat. No. 2,193,138, Int. Cl. E 21 C 35/06, publ. Feb. 15, 1974), comprising a base plate; a first carriage mounted on the base-plate; a trough-shaped carrier secured to the first carriage for rotation about the vertical axis; a boom extending in parallel with the longitudinal axis of the baseplate mounted for rotation on the trough-shaped carrier about the horizontal axis and about its own longitudinal axis; a platform mounted on the boom for rotation about a horizontal pivot pin mounted on, or adjacent to the outer end of the boom; a second carriage for installation of the implement, which is mounted for sliding with respect to the platform.
The first carriage is movable longitudinally along the baseplate by means of double-action hydraulic jacks.
The trough-shaped carrier is rotatable about the vertical axis with respect to the first carriage on which it is mounted by means of double-action hydraulic jacks.
The boom mounted on the trough-shaped carrier is rotatable about the horizontal axis up and down under the action of a pair of double-action hydraulic jacks. In addition, the boom is rotatable about its own longitudinal axis by a hydraulic drive.
The platform is mounted on the front end part of the boom for rotation with respect to the boom under the action of respective double-action hydraulic jacks.
The second carriage, which is mounted on the platform and designed for the installation of the implement, is movable by a double-action hydraulic jacks along the longitudinal axis of the platform.
All jacks are actuated by a hydraulic system including an oil tank, a pump having a drive, a system of pipelines, various control and safety valves. The hydraulic system is manually controlled from the operator's workplace on the trough-shaped carrier.
By moving the abovementioned members, the implement is brought up to, and pressed with its tool against the rock at a point where the rock is to be broken down. Then the hammer piston of the implement delivers a blow at the tool which transmits the impact energy to the rock thereby breaking it. After a rock lump is broken away, the implement is set to a new position, and the next blow is delivered.
The broken rock is removed by means of a scraper and winch.
The abovedescribed machine for driving workings in hard rocks is rather a sophisticated apparatus having a large number of hydraulic jacks and pivotal joints. The percussive implement used in the machine has to be positioned in such a manner that its longitudinal axis and the axis of the tool aligned therewith should be directed substantially at right angles to the surface of the rock body at a point where a blow is to be delivered. When a lump of rock falls down after the blow, the end of the tool acting upon the rock may slip over the surface of the rock body at an angle substantially different from the right angle. This slippage can be the cause of substantial dynamic loads acting upon all members of the machine which are only limited by the amount of yielding of these members so that they can fail.
The complicated structure of the machine and the abovedescribed phenomenon of slippage of the implement tool substantially lower reliability of the machine.
The need to set the implement every time at right angles to the rock body entails substantial downtime for setting the implement before each blow so that efficiency of rock breaking is rather low.
Also known in the art is a machine for driving workings in hard rocks (cf. U.S. Pat. No. 4,300,802, Int. Cl. E 21 C 29/28, publ. Nov. 17, 1981), comprising a movable carrier which can move over the working floor and which is the base member for supporting all other members of the machine. Installed on this carrier is a fork-shaped boom mounted for rotation in a horizontal plane with respect to the carrier by means of two hydraulic cylinders. A frame is mounted between the legs of the boom for rotation in a vertical plane with respect to the boom under the action of two other hydraulic cylinders. The frame has four openings with guide surfaces in its walls, and support members are slidable along the guide surfaces. The support members have holes in which are rotatably received pins on which an implement is mounted. The implement is in the form of a high-energy "shot"-type implement, i.e. one in which the hammer piston does not touch the rock face of a working being driven before the moment the blow is delivered.
Two groups of shock-absorbing means are secured to the frame symmetrically with respect to a plane drawn at right angles to the implement longitudinal axis and passing along the axes of the pins in such a manner that each of the support members is held on either side against sliding along the guide surfaces by tappets of said shock-absorbing means.
The shock-absorbing means are intended to reduce forces transmitted from the implement to the other members of the machine in case of oblique blows and idle strokes of the hammer piston of the implement, as well as to maintain the present direction of the longitudinal axis of the implement after occurrence of such phenomena. Each shock-absorbing means comprises two oppositely arranged pneumatic cylinders whose rods are essentially tappets provided with pistons entering cylinder spaces filled with a compressed gas.
In the process of the implement operation a considerable part of blows delivered by the hammer piston thereof at the face are oblique ones, i.e. such blows the direction of which does not coincide with the normal to the rock surface in the spot the blow is delivered to. The oblique blow is always followed by a lateral recoil. In case of a lateral recoil in a horizontal plane the implement turns about its vertical axis on a pair of respective pins rotating in the support members located above and below the implement. The support members located on the sides of the implement slide in their guides and act upon the tappets of the shock-absorbing means. At the end of lateral recoil when the implement rotation ceases, the implement acted upon by the shock-absorbing means turns in the opposite direction. The lateral recoil in a vertical plane happens in the similar way. If the lateral recoil occurs in a plane laying between the horizontal and vertical planes, two vertical and two horizontal shock-absorbing means jointly come into play.
When the hammer piston performs an idle stroke fully or partly, i.e. when the hammer piston does not hit at the rock face during its forward movement, or if the hammer piston does not have time to spend its energy completely for breaking the rock, the implement will tend to move forward to follow the hammer piston and will act, through its pins and support members put thereon, upon the tappets of the front-end group of the shock-absorbing means. After the implement movement is completed, the reverse process takes place and, under the action of the tappets of the front-end group of the shock-absorbing means, the implement is returned to its initial position.
In the abovedescribed situations, when a force is applied to the tappet of the shock-absorbing means, the tappet moves within a cylindrical space and additionally compresses with its piston compressed gas which is available in that space. Any lateral recoil or idle stroke of the implement will be thus dampened by compression of gas in the cylindrical space of the shock-absorbing means. Under the action of the compressed gas the tappets will return the implement into the initial position.
It should be, however, noted that when the shock-absorbing means are actuated, e.g. upon a lateral recoil, the compressed gas, when additionally compressed by the tappet piston, accumulates a considerable amount of energy and will give it up when the implement is returned into the initial position. This will result in the implement arriving at the initial position after gaining a substantial speed so that it will move further past the initial position and will act upon the opposite tappet, i.e. damped oscillations of the implement will occur. The oscillatory process will on the one hand result in a longer time of return of the implement to its initial position and, one the other hand, it will cause an increase in the rate of wear of the shock-absorbing means. this disadvantage is conducive to a lower efficiency and shorter service life of the machine.